The skin serves as an important boundary between the internal milieu and the environment, preventing contact with potentially harmful antigens. In the case of antigen/pathogen pentetration, an inflammatory response is induced to eliminate the antigen. This response leads to a dermal infiltrate that consists predominantly of T cells, polymophonuclear cells, and macrophages (see, e.g., Williams and Kupper (1996) Life Sci., 58:1485-1507.) Normally, this inflammatory response, triggered by the pathogen, is under tight control and will be halted upon elimination of the pathogen.
In certain cases, this inflammatory response occurs without external stimuli and without proper controls, leading to cutaneous inflammation. Cutaneous inflammation, the result of the cellular infiltrate noted above as well as the secreted cytokines from these cells, encompasses several inflammatory disorders such as cicatricial pemphigoid, scleroderma, hidradenitis suppurativa, toxic epidermal necrolysis, acne, osteitis, graft vs. host disease (GvHD), pyroderma gangrenosum, and Behcet's Syndrome (see, e.g., Willams and Griffiths (2002) Clin. Exp. Dermatol., 27:585-590). The most common form of cutaneous inflammation is psoriasis.
Psoriasis is characterized by T cell mediated hyperproliferation of keratinocytes coupled with an inflammatory infiltrate. The disease has certain distinct by overlapping clinical phenotypes including chronic plaque lesions, skin eruptions, and pustular lesions (see, e.g., Gudjonsson, et al. (2004) Clin Exp. Immunol. 135:1-8). Approximately 10% of psoriasis patients develop arthritis. The disease has a strong but complex genetic predisposition, with 60% concordance in monozygotic twins.
The typical psoriatic lesion is a well defined erthematous plaque covered by thick, silvery scales. The inflammation and hyperproliferation of psoriatic tissue is associated with a different histological, antigenic, and cytokine profile than normal skin. Among the cytokines associated with psoriasis are: TNFα, IL-18, IL-15, IL-12, IL-7, IFNγ, IL-17A and IL-23 (see, Gudjonsson, et al., supra). IL-17A has been detected in psoriatic skin and is know to mediate keratinocyte proliferation.
To date, prediction of psoriasis flare-ups has been hampered by lack of knowledge of the cytokine changes between nonlesional and lesional psoriatic tissue. The present invention fills this unmet need by providing a method of comparing IL-17A and IL-17F expression in nonlesional psoriatic skin relative to normal skin, thus affording the ability to assess probability of the formation of lesional psoriasis.